Traveling vehicle system and communication method in the traveling vehicle system

Abstract

A system server and access points are connected through a LAN preferably on the ground. A control cycle is divided into an instruction time zone to provide instructions from the access points to traveling vehicles, and a report time zone to provide reports from the traveling vehicles to the access points. The access points transmit target positions in the instruction time zone, and the traveling vehicles report positions in the report time zone. The system server determines target positions based on the reported positions.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a traveling vehicle system. In particular, the present invention relates to a system in which a large number of traveling vehicles are controlled by a system server through a wireless LAN.2. Description of the Related ArtThe applicant proposed a system in which a large number of traveling vehicles such as overhead traveling vehicles are controlled by a system server on the ground. See, for example, JP2008-150135A. In this system, the system server provides an instruction of a target position or the like for each traveling vehicle in each control cycle of, e.g., 0.1 s, for allowing the traveling vehicle to execute the instruction. A wireless LAN is used suitably for communication between the traveling vehicles and the system server. In this system, although the wireless LAN is used, it is important to ensure that the instructions from the system server to the traveling vehicles do not have any delay,...

AI Technical Summary

Benefits of technology

Preferred embodiments of the present invention carry out communication between a system server and traveling vehicles efficiently, prevent relative positions between traveling vehicles from being affected by delays in communication, and allow traveling vehicles to report to access points efficiently.

In a preferred embodiment of the present invention, the instruction time zone and the report time zone are preferably provided in each control cycle. In the instruction time zone, the traveling vehicle only transmits a confirmation signal or the like, without performing any communication that may interfere with the instruction from the access point. Therefore, the access point can provide a position instruction for the traveling vehicle in the instruction time zone efficiently. Further, the traveling vehicle reports a position in the report time zone. Based on the reported position, the system server can generate the next target position. In this manner, the system server can control the traveling vehicle through the wireless LAN.

In particular, preferably, a plurality of the traveling vehicles generate reports at a common time, and execute instructions at the common time, i.e., simultaneously. In this manner, the system server can recognize relative positions between the traveling vehicles without being affected by delays in data transmission or the like. Further, even if there is any delay in reception or the like, the relative positions between the traveling vehicles can be maintained.

In particular, preferably, the report time zone is divided into a plurality of time slots, and the traveling vehicle includes a selector arranged to randomly select one of the plurality of time slots to transmit the report to the access point in the selected time slot. Preferably, in the report time zone, interference between reports from the traveling vehicles, i.e., collision between reporting packets should be prevented. For this purpose, for example, the order of reports may be designated in the instructions. However, in this case, the load on the access point is increased. Therefore, the report time zone is preferably divided into a plurality of time slots, and each of the traveling vehicles randomly selects one of the time slots. In this manner, the order of reports can be determined autonomously. Moreover, by increasing the number of time slots, the probability of collision between reports becomes small. Since the time slot is selected randomly, the traveling vehicles can be treated fairly.

Problems solved by technology

If the instructions or the reports are delayed, the system server cannot control the traveling vehicles in real time.

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